1. Technical Field
The present disclosure relates to a shock absorber damping vibrations transmitted from a road surface to a vehicle and, more particularly, to an amplitude selective shock absorber that provides a low-damping force characteristic in response to input of high frequency vibrations, which have low amplitudes and occur frequently, thereby enhancing ride comfort of a vehicle.
2. Description of the Related Art
In general, a vehicle is provided with a suspension system for enhancing ride comfort by absorbing or relieving impacts or vibrations transmitted from a road surface to an axle while traveling on the road. One component of the suspension system is a shock absorber. The shock absorber is disposed between the axle and a vehicle body, and includes a cylinder and a piston rod movable in the cylinder. The cylinder is filled with a damping fluid such as gas or oil, which is moved by a piston valve secured to one end of the piston rod to generate a damping force.
As such, a conventional shock absorber has a restriction in that it exhibits predetermined damping force characteristics according to variation of a road state or a driving posture of a vehicle. In other words, a low damping force characteristic can improve driving comfort of the vehicle, but cannot maintain a stable driving posture thereof. Conversely, a high damping force characteristic can maintain the stable driving posture of the vehicle, but entails deterioration in ride comfort. As such, the conventional shock absorber is incapable of controlling damping force characteristics in response to variation of the road state or the driving posture of the vehicle.
In order to solve the problem of such a conventional shock absorber, an amplitude selective shock absorber has been developed to provide variable damping force characteristics according to displacement of the piston rod.
FIG. 1 is a cross-sectional view of a portion of a conventional amplitude selective shock absorber capable of providing variable damping force characteristics according to displacement of a piston rod.
Referring to FIG. 1, the existing amplitude selective shock absorber includes a cylinder 10, a piston rod 20 axially movable within the cylinder 10, a stationary piston valve 30 fixedly mounted on the piston rod 20 to divide a space of the cylinder 10 into a rebound chamber and a compression chamber, and a floating piston valve 40 mounted on the piston rod 20 to be movable in an axial direction inside the rebound chamber.
A stopper 50 is secured to the piston rod 20 above the floating piston valve 40. Return spring 60 and stop springs 70 are interposed between the floating piston valve 40 and the stationary piston valve 30 and between the floating piston valve 40 and the stopper 50, respectively.
A length from an upper end of the stationary piston valve 40 to a lower end of the stopper 50 is determined according to a desired design of a final product.
Conventionally, the return springs 60 and the stop springs 70 are disposed between the floating piston valve 40 and the stationary piston valve 30 and between the floating piston valve 40 and the stopper 50. Since the return spring 60 and the stop spring 70 are coil-type springs, they are substantially lengthy. Accordingly, if the length from the upper end of the stationary piston valve 40 to the lower end of the stopper 50 is set small according to a desired design of a final product, the floating piston valve 40 cannot be mounted to the amplitude selective shock absorber.
As clearly shown in FIGS. 2 and 3, in the conventional amplitude selective shock absorber, the floating piston valve 40 includes an annular valve body 41 having fluid passage holes 41a; a pair of upper and lower valve discs 43 mounted on upper and lower sides of the valve body 41 to generate a damping force, respectively; a pair of upper and lower coil-wave type valve springs 45 mounted on upper and lower sides of the upper and lower valve discs 43 to compress the valve discs 43, respectively; and a pair of upper and lower coupling supports 47 coupled to the valve body 41 through an upper side of the upper coil-wave type valve spring 45 and a lower side of the lower coil-wave type valve spring 45 to hold the valve discs 43 and the coil-wave type valve springs 45 between the coupling supports 47 and the valve body 41, respectively.
Conventionally, each of the coupling supports 47 is composed of an annular support section 47a and coupling sections 47b formed on an overall inner edge of the annular support section 47a. When coupled to the valve body 41, the coupling sections 47b are inserted into an inner diameter of the valve body 41 while adjoining the inner diameter of the valve body 41, so that the inner diameter of the valve body 41 inevitably increases corresponding to the thicknesses of the coupling sections 47b of the coupling support 47. Accordingly, an interface between an annular section of the valve body 41 and the annular support section 47a of the coupling support 47 is decreased in area by an increased amount of the inner diameter of the valve body 41, so that the widths of the valve discs 43 are decreased by the increased amount of the inner diameter of the valve body 41. As a result, as valve springs to be disposed between the valve body 41 and the coupling supports 47 to compress the valve discs 43, the conventional floating piston valve employs the coil-wave type valve springs 45 which are expensive and require a narrow mounting area instead of tripod type leaf valve springs which are inexpensive and require a large mounting area.